mapreduce解析执行sql流程

样例准备

编号	姓名	性别	班级编号
1	name_1	male	1
2	name_2	female	2
3	name_3	male	3
4	name_4	female	4
5	name_5	male	1
6	name_6	female	2
7	name_7	male	3
8	name_8	female	4
9	name_9	male	1
10	name_10	female	2
11	name_11	male	3
12	name_12	female	4
13	name_13	male	1
14	name_14	female	2
15	name_15	male	3
16	name_16	female	4
17	name_17	male	1
18	name_18	female	2
19	name_19	male	3
20	name_20	female	4
21	name_21	male	1
22	name_22	female	2
23	name_23	male	3

班级编号	名称
1	服装
2	机械
3	计算机
5	航天

条件过滤

sql：select * from student where sex='male';

mr：该操作属于比较简单的操作，直接在map阶段对数据进行过滤操作即可。

分组统计

sql：select class_name,count(*) from student group by class_name;

mr：

表联接